1. Field of the Invention
The present disclosure relates to a method for preparing polymer foam and, more particularly to a method for preparing polymer foam via a pressure-induced flow (PIF) process.
2. Description of Related Art
Polymer foam, especially polypropylene foam, has many industrial applications, and the global polymer foam market has witnessed a rapid growth in the past few years.
Polypropylene (PP), as one of the most widely used commercial polymers, has many desirable properties, such as high melting point, good plasticity, low density, excellent chemical resistance and food safety, and easy recycling. These outstanding properties as well as a low material cost have made PP more competitive in producing plastics and foam products than other thermoplastics in various industrial applications. However, like other commodity polymers, the low thermal stability and mechanical strength prevent PP from many engineering and structural applications. Furthermore, its low melt strength leads to cell rupture and low expansion ratio in the melt foaming process unless long-chain branching, polymer compounding, or chemical crosslinking are used to modify PP.
However, PP is very difficult to be foamed because of its low melt strength and high crystallinity. Many methods such as polymer blends, composites, and copolymerization have been used to achieve good expandable PP and PP foams. However, these methods face limited applications owning to the significant cost increase in materials and poor mechanical strength of foamed products in comparison with PP and other widely used foam materials such as polystyrene (PS).
Hence, it is desirable to provide a novel method for preparing polymer foam, especially PP foam, which can manufacture polymer foam in a promising and feasible way; and therefore, the obtained polymer foam can be successfully used in industrial applications.